(i) Field of the Invention
The present invention relates to a radio wave transmitting material, particularly to a radio wave transmitting material which is mounted on a front surface of a radio wave absorbent material for use in a radio wave absorptive wall, and the like.
(ii) Description of the Related Art
Recently, toward the realization of a high information society, the application of radio waves has been rapidly enlarged centering on a mobile communication field. Moreover, with an innovative progress of today""s microelectronics technique, various electronic apparatuses have been prevalent. However, with the development of such information communication technique, the influence of unnecessary electromagnetic noises exerted onto precision apparatus associated devices has raised problems.
For the measurement of electromagnetic noises, a radio wave dark room (anechoic room) where there is no reflection of electromagnetic waves is used, and a radio wave absorbent material is used in an inner wall of the radio wave dark room. Examples of the radio wave absorbent material for use in the radio wave dark room include a radio wave absorbent material which is constituted of foamed styrene, foamed urethane, or another organic material and which has a square pole shape, or a wedge shape.
However, since the radio wave absorbent material is blended with carbon black, and the like to obtain a conductivity, the radio wave dark room provides a dark and oppressed feeling inside. Moreover, since an apex of the radio wave absorbent material in the shape of the square pole or the wedge is relatively brittle, there is a problem that the material is easily broken by collision, and the like. Furthermore, with an increase of radio wave troubles, an immunity test and another large-power test are turned to a direction in which they are obliged to be performed. In the radio wave dark room which is used in a closed state, from the viewpoint of an enhanced safety, incombustible materials are requested to be used.
To solve the problems, apex sites (front surfaces) of a multiplicity of arranged radio wave absorbent materials are covered with a white radio wave transmitting material which is lightweight and which has a property of transmitting radio waves. However, in the conventional radio wave transmitting material, a foamed board of foamed styrene and another plastic is used, but these are not incombustible materials.
Moreover, as the radio wave transmitting material provided with incombustibility, a foamed board of calcium carbonate, and a nonwoven board of ceramic fiber are developed. However, the former is in a quasi-incombustible level, and is insufficient from the viewpoint of safety. Moreover, the latter is superior in incombustibility but expensive, which has a problem that a reduction of manufacture costs of the radio wave dark room is hindered.
An object of the present invention is to provide a radio wave transmitting material to be mounted on a front surface of a radio wave absorbent material for use in a radio wave dark room, a radio wave absorptive wall, and the like, which is lightweight and superior in incombustibility and radio wave transmittance.
To attain this and other objects, according to the present invention there is provided a radio wave transmitting material which comprises a honeycomb structure, and incombustible boards bonded integrally to opposite surfaces of the honeycomb structure using an adhesive. The honeycomb structure is formed by laminating incombustible sheets prepared from a slurry containing a main component of an inorganic hydrate compound into a honeycomb shape using an inorganic adhesive, and the incombustible boards are prepared from the slurry containing the main component of the inorganic hydrate compound.
In the present invention, the honeycomb structure is lightweight but provides superior incombustibility and radio wave transmittance, and the incombustible board imparts a superior mechanical strength and incombustibility to the radio wave transmitting material. Therefore, the radio wave transmitting material of the present invention is lightweight and is provided with the superior incombustibility and radio wave transmittance. Moreover, the radio wave transmitting material is also excellent in mechanical strength, and can protect a plurality of radio wave absorbent materials arranged in the radio wave dark room, and the like without generating any radio wave reflection. Furthermore, since the incombustible board has a white color, no oppressed feeling is provided inside the radio wave dark room.